Polyurethane products are produced by reacting active hydrogen containing materials with isocyanates. Their physical properties are determined by the molecular structure of the resultant polymer. Accordingly, polyurethane products having a wide variety of properties may be prepared with the use of different active hydrogen containing compounds, isocyanate compounds, and select additives. While the word polyurethane is inclusive and is used for all polymers containing urethane linkages, it should be noted that the polymers themselves usually also contain other linkages. Essentially, there are seven major types of linkages in polyurethane polymers, namely: urethane, urea, biuret, allophanate, acyl urea, uretone and isocyanurate.
The properties of urethane polymers will necessarily depend on factors such as the active hydrogen containing compound, the isocyanate type, the catalysts, the degree of cross-linking, and the processing conditions. Most of the mechanical properties will change with the molecular weight of the polymer, as well as the molecular weight per cross-link or branch point. The urethane formation reaction is excellent for extending the polymer growth, whereas, reactions forming the allophanate, biuret, and acyl urea linkages increase the molecular weight per cross-link in the polymer. With a good knowledge of the correlation between properties and polymer structure, a wide variety of urethane products can be produced and tailored to meet the requirements of many applications.
Catalysis is generally required to promote the reactions of isocyanate and compounds containing active hydrogen. The catalysts commonly employed today consist of tertiary amines such as triethylenediamine and tin catalysts such as stannous octoate. (See, e.g. U.S. Pat. Nos. 3,822,223 and 3,397,158.) At low temperatures the tertiary amine will generally promote reactions between isocyanate and water, while the tin catalysts will generally promote the reaction between isocyanates and active hydrogen atoms.
Since the role of catalysis in flexible polyether polyurethane foam preparation is well known with tin-amine catalyst systems, the changes in foam technology during recent years have generally been directed to changes in active hydrogen containing compounds and isocyanates. The flexible foams are usually made using 105-115% of the equivalent amount of isocyanate required for reaction with all the active hydrogen groups of any polyol, amine and water of the formulation, and most preferably using about 110% of the stoichiometric amount. This percentage corresponds to an isocyanate index of from 105 to 115. The isocyanate index is defined as the ratio of the amount of isocyanate actually used to the amount of isocyanate theoretically required to react with all of the active hydrogen groups. The excess of isocyanate is generally employed in the formulation to: (a) assure complete reaction of the reactants, and (b) to obtain higher load bearing properties in the foam through cross-linking reactions during foam cure. Using isocyanate concentrations in excess of 115% of equivalent amount has not been generally feasible using the tin-amine catalyst systems because it generally resulted in processing problems such as foam splits, shrinkage, inadequate cure rate, and excessive isocyanate vapors during production. Accordingly, it is evident that a catalyst system is needed that will overcome these problems by increasing the rate of reaction between the isocyanate and the active hydrogen of the initial reaction products of the reaction mixture.
Many different approaches have been made to providing such catalyst systems. Thus, it has been suggested to utilize an alkali or alkaline earth metal hydroxide, carbonate, siliconate, carboxylic acid salt or fatty acid salt in combination with a tertiary amine (see, e.g., Canadian Pat. No. 927,050). Additionally, the art has suggested a wide variety of different metal compounds for use as a catalyst including (a) combinations of an organo-alkaline earth metal with a non-aromatic tertiary chelating diamine (see, e.g., Canadian Pat. No. 827,659); (b) mixtures of mercuric salts and a basic metal compound (see, e.g., U.S. Pat. No. 3,395,108); (c) alcoholates and salts of alkaline earth and alkali metals (see, e.g., U.S. Pat. No. 3,205,201); (d) hydroxides or weak acid salts of alkali metal, alkaline earth metals or of a fully substituted quaternary ammonium, phosphonium or tertiary sulphonium radicals, in combination with tin compounds (see, e.g., U.S. Pat. No. 3,108,975); (e) mixtures of tin, lead and zinc naphthenates and octoates (see, e.g., U.S. Pat. No. 3,347,804); and (f) carboxylic acid salts of lead, mercury, tin, bismuth or antimony (see, e.g. Canadian Pat. No. 757,695). Finally, it has been proposed to combine various stannous salts such as stannous octoate, with various metallic soaps such as barium stearate, calcium stearate, calcium naphthenate, aluminum stearate, cadmium stearate and the like (see, e.g., U.S. Pat. Nos. 3,342,757 and 3,391,091). Although U.S. Pat. No. 3,342,757 indicates that calcium naphthenate, e.g., may be combined with a tertiary amine, nothing contained in the disclosure would indicate any benefit to be accomplished therefrom.
So far as Applicant is aware, the prior art does not describe the use of any barium or calcium salts of carboxylic acids, to catalyze the polyurethane reaction and, in particular, to specifically catalyze side reactions such as allophanate formation. However, barium sulfate and calcium carbonate are known as inorganic fillers for cutting costs, improving or providing appropriate physical properties in, for example, carpet-backing and in making flexible foam. In Saunders & Frisch, High Polymers, Vol. XVI, Polyurethanes, Chemistry and Technology, Part I, pp 169 ff, barium and calcium acetate are mentioned as possible catalysts for the isocyanate-hydroxyl reaction, but were found to yield gellation times in excess of 240 minutes.